The present invention relates generally to electronic circuits. More particularly, embodiments of the present invention relate to the field of integrated oscillator circuits for controllers and, in particular, controllers for ultra-low power battery applications.
Integrated circuit oscillators are often used in (micro)-controller circuits. In addition, integrated oscillators are also used to provide clock signals and ramp signals (or sawtooth signals) in pulse width modulation (PWM) based systems, such as those used in switch mode power supplies (SMPS) and amplifier circuits.
FIG. 1 is a simplified block diagram illustrating a system 100, in which a controller is configured for frequent power-on and power-off operations. In this example, the (micro)-controller circuit 110 is in a power down state, while it monitors the state of a terminal GPIO1. In this example, GPIO1 is connected to a temperature actuated switch 120, which trips at a preset temperature. An LED (light-emitting-diode) 130 is used to indicate when the temperature actuated switch has tripped, based on operations performed by the controller core. When the temperature actuated switch trips, the logic powers up the controller. As shown in FIG. 1, The GPIO1 signal is passed through a debounce filter 112 in order to ensure that the switch has completely changed state to avoid false indications and waste of power through the LED. The debounce filter is coupled to an oscillator 114 for the debounce timer. This debounce filter 112 is continuously monitoring the GPIO, and the oscillator 114 is continuously running while the controller is in a power down state. Therefore, for long battery life, an ultra low power debounce filter and oscillator is desired.
Some conventional integrated circuit oscillators use ring oscillators, with resistors, capacitors, inductors, crystals and MOS invertor stages. These ring oscillators often use precision external voltage and current references. Other conventional integrated circuit oscillators use capacitor charging circuit, but also may rely on external reference circuits and control circuits.